Drill strings of pipe for oil and gas wells are assembled or disassembled vertically on a derrick one joint at a time, and are stored horizontally on pipe racks situated on the ground adjacent the rig. The work floor of the rig is typically elevated substantially above the pipe rack such that transferring sections of pipe to and from the work floor and the racks is necessary and requires careful handling of the heavy pipe to protect the workers and the pipe.
As shown in FIG. 1, a common prior art solution in the context of a transportable trailer is a pipe handling apparatus implementing a base supporting a pivoting boom having a pipe receiving trough along its upper surface. The boom has an upper end which can be placed adjacent to and raised to the height H of a derrick or rig floor (not shown), and a lower end which is movable along the base. Typically the lower end is guided in a cavity in the base which also serves to receive the boom therein when lowered. An arm pivots between the base and the boom for raising the boom from the base to the floor height. At the end of a pipe lowering operation, as well as during transport or storage, the boom is retracted to nest into the cavity.
Although effective to raise the upper end to a predetermined height H, this type of prior art pipe handling apparatus does not readily permit adaptation to raise the upper end to a range of different rig floor heights. Through some extreme manipulation, this prior art apparatus can accomplish a lower than usual design elevation of the booms upper end by re-positioning the base, spaced further back from the rig floor than normal, and then over-extending the pivoting arm towards the floor to an obtuse angle relative to the base. However, in such a case the end of the pivoting arm attached to the boom travels well over the point at which it is pivoted from the base. This in turn increases hydraulic actuator travel, requiring a more expensive type of double-acting hydraulic ram, also capable of pulling a load upon it's return and under a more onerous mechanical disadvantage. The increase in hydraulic travel also requires more time and may not allow the apparatus to keep pace with the pipe handling crew thereby resulting in decreased productivity. The over-extension of the arm also raises additional wear-and-tear, maintenance, safety and structural concerns.
Limitation to a predetermined height H, inherent in the prior art apparatus, is not typically a disadvantage for pipe handling apparatus used by one particular oil or gas drilling company; since a company tends to have all their rig floors at a set height. However in many cases, such as with rental oil field equipment, pipe handling apparatus can services a plurality of different clients having derrick or rig floors at different heights when compared to each other.
There is a demonstrated needed for a pipe handling system wherein the boom can be raised to meet with a range of derrick or rig floor heights without the disadvantages of the prior art.